1. Field of the Invention
The present invention relates to the field of motion sensing in electromechanical assemblies and machines. More particularly, the invention relates to shock sensing in the field of Hard Drive Assembly (HDA), such as hard disk drives used in computer magnetic recording apparatus.
2. Background Art
As portable personal computers (PCs) such as laptop and notebook-sized computers become ubiquitous, it has become important for HDA designers to identify and eliminate the portable PCs' most common failure causes to improve their reliability. Generally, portable computers are subject to some types of failure which would not be a problem for desk top machines. For example, portable computers can be dropped while being carried or worked on, and components in the portable system can be damaged or crippled. One of the leading failure causes for portable PCs is in the fragility of the disk drive and its shock vulnerability.
Hard disks play an important part in delivering the same power and functionality of desk top computers for portable personal computers. In disk drives, a typical Hard Drive Assembly (HDA) comprises one or more rotatably mounted disks having an extremely thin magnetic coating deposited on the disk substrate. Information is generally read and written from the hard disks by a read/write head. An HDA typically has a very sensitive architecture wherein a very small gap is maintained between the drive head and the disk, and this makes the HDA especially vulnerable to shock damage. Since the smaller this gap is, the more data a hard disk can store, small gap dimensions are the norm for the hard disks.
Thus, in disk drive applications, it is important to protect Hard Drive Assembly (HDA) from environmental shocks and hazards. Disk manufacturers understand this problem and usually deal with it by shock mounting the HDA. Still, physical or mechanical impact can destroy the data integrity or hardware integrity of a hard disk. For example, when excessive shocks severely damage or cripple hard disk drives, users are at potential risk of not only having to replace the damaged drives but also losing valuable database.
Whenever excessive shocks occur, therefore, writing to disk drives must be prohibited to maintain data integrity on drives and prevent any damages to the drives. A shock detector can be used for this purpose to sense and detect excessive shocks, and signal an embedded microprocessor to stop writing on disk drives.
Traditionally, the HDA shock detector is implemented with discrete components including resistor and capacitor components. However, using a number of discrete components not only compromises the performance of detection circuitry for cost, but also takes a fair amount of board space to accommodate discrete components. A bulkier board usually increases costs due to various factors such as higher board cost and packaging cost. A bulkier size could also mean that there is a greater possibility in the system that some components would fail, and thus less overall system reliability.
Prior art RC-active filters also do not achieve steep attenuation of the input signals below the half-power or -3 dB frequencies. FIG. 1 shows a typical prior art front-end filter implemented by using discrete components. The filter has two real poles and one transmission zero at zero frequency. Shock sensor 101 and resistor 103 of 10 M.OMEGA. are coupled in parallel via capacitor 105 to the positive input terminal of amplifier 115. The positive input terminal of amplifier 115 is also coupled via resistor 107 and bypass capacitor 109 to a circuit reference point such as circuit ground. Capacitor 119 and resistor 117 are coupled between the output terminal of amplifier 115 and the negative input terminal of amplifier 115 in parallel. The negative input terminal of amplifier 115 is also coupled via resistor 111 and bypass capacitor 113 to a circuit reference point such as circuit ground.
In FIG. 1, the capacitor 105 provides AC-coupling for the shock signal input and blocks out DC component. The filter circuit shown in FIG. 1 provides sufficient rejection on DC component and a gain boost in the passband. But the rejection on high-frequency components is not acceptable for most HDA applications. To overcome this deficiency requires a higher-order filter, which can provide better high-frequency response characteristics. However, this increases the cost and the board space.
Further, RC-active circuits utilizing operational amplifiers with resistors and capacitors show unstable frequency response characteristics because the filter characteristics are dependent on resistor and capacitor values. To compound the problem, typical shock filter characteristics require large-value resistors and capacitors to realize low-frequency poles and zeros, which in turn occupy relatively large silicon space in integrated circuit technology. Thus, prior art RC-active circuits are not suitable for monolithic integration using, for example, CMOS technology, thereby making it difficult to scale down the system.
Furthermore, most prior art shock detectors are designed to detect only one-axis shock for the sake of simplicity and low cost. While this method is satisfactory for some applications, often it is not adequate or sufficient to detect and compensate for excessive shocks and protect the hard disk drives. A one-axis shock detector, for example, will not have a complete shock detection since shock signal is detected only along one axis, and consequently will result in less accurate sensing of actual physical or mechanical shock than desired. While less accurate shock sensing might be tolerable for desk top computers and work stations, they can often cause critical damage or crippling effect for many portable personal computers such as laptop computers.
However, if one were to design a two-axis shock detection system to provide more accurate sensing using prior art discrete component system, it would require even bigger board space and the compact size would have to be traded off for accuracy. FIG. 2 shows a conventional full-wave rectifier with summer and LPF implemented by discrete components. Referring to FIG. 2, input signal VINx is coupled to X-axis full-wave rectifier 211, which is coupled to summer 215 through resistor 219. The output of summer 215 is coupled to LPF217, which outputs to Vout. VINy is coupled to Y-axis full-wave rectifier 213, which is also coupled to summer 215 through resistor 221.
Shock signals from two-axis need to be full-wave rectified individually prior to being added together since the shock can be in either positive or negative direction of either axis. As shown in FIG. 2, conventionally, two diodes are used to rectify the current in one direction. Not only is the approach unsuitable for CMOS implementation, but also requires a fair amount of silicon area. As discussed, a bulky design adds to costs and is not suitable for portable computer applications.
Thus, there is a need in the art to overcome the shortcomings of the prior art HDA shock detector and provide a shock detector that can be fabricated in compact size by monolithic integration technology and still deliver an improved and reliable shock sensing capability. The present invention provides such fully integrated design for a two-axis HDA shock detector.